1. Field of the Invention
This invention relates to controls for brake systems for multiple vehicle systems (i.e. tractor-trailer vehicles). In particular, this invention relates to brake system controls mounted on the trailer only which will distribute the braking effort between the vehicle brake sites, such as between the sub-vehicle brake systems, to achieve inter-tractor-trailer proportional braking.
2. Description of the Prior Art
Brake systems, and the controls therefore, for vehicles, including heavy duty vehicles such as trucks, are, of course, well known in the prior art.
Brake systems for passenger cars are, in general, somewhat easier to design than brake systems for heavy duty vehicles such as trucks as the loading of passenger vehicles will not vary to the extent loading will vary on the tractor of a tractor-trailer which may comprise a tractor only, a tractor with an empty or lightly loaded trailer or a tractor with a heavily loaded trailer.
Brake systems of the anti-lock type, for all types of vehicles, are well known in the prior art. Briefly, these systems operate to obtain a maximized vehicle stability (i.e. maximized transverse coefficient of friction of braked wheels) by maintaining the longitudinal slip of the braked wheels within predetermined limits. This usually requires modulating the braking forces on an individual wheel and/or individual axle basis to maintain at least some wheel rotation.
Examples of prior art anti-lock systems may be seen by reference to U.S. Pat. Nos. 3,767,270; 3,768,872; 3,854,556; 3,893,696; 3,929,383; 3,929,382; 3,966,267; 4,392,202 and 4,591,213, the disclosures of all of which are hereby incorporated by reference.
Brake systems which control braking to achieve a driver demand, sensed driver demand in "brake-by-wire" manner, sense coefficient of friction and modified brake forces accordingly, sense load on a wheel and modified braking effort accordingly, sense wheel slip and/or used electronic signals to achieve more rapid trailer brake response are also disclosed in the prior art as may be seen by reference to U.S. Pat. Nos. 4,140,352; 4,327,414; 4,494,199; 4,512,615; 4,545,240; 4,591,213; 4,606,586; 4,616,881; and 4,648,663, the disclosures of which are hereby incorporated by reference.
While the prior art brake systems which modify braking effort in response to sensed parameters to achieve various goals, such as vehicle stability or the like, do, in general, provide enhanced vehicle braking, they are subject to further improvement. In the prior art systems for tractor-trailer vehicles, if braking effort between the tractor and trailer is to be controlled in a predetermined manner, specially configured and equipped tractors and trailers were required.